The present invention is directed generally to optical transmission systems. More particularly, the invention relates to optical transmission systems including protection capability for use in optical communication systems.
Communications transport systems are used to transport information over a substantial portion of the world. This extensive communication access requires enormous amounts of equipment to provide the necessary infrastructure for the systems. In addition, much of the equipment and almost all of the transport media is remotely located and necessarily exposed to the environment.
The necessary exposure of transmission equipment and systems to uncontrolled environments increases the likelihood for failures to occur. However, if communication systems are to be effective it is necessary to have a high degree of reliability in the system. The reliability of service provided by a transmission system is inversely proportional to the frequency of failures in the transmission system.
One of the most common failures in fiber optic transmission systems is a fiber break. When a fiber break or other failure occurs in a transmission link, the traffic intended to pass through the link must be rerouted through another path until the link is restored. Another common source of failures in optical transmission systems is an equipment failure. The amount of traffic that is lost upon an equipment failure depends upon the particular piece of failed equipment in the system. For example, in most, if not all, currently available fiber optic transmission systems, a line amplifier failure will result in a complete loss of traffic traveling through an optical link containing the failed line amplifier. Whereas, a transmitter or a receiver failure will generally result only in the loss of the traffic carried by wavelengths associated with the failed transmitter or receiver. When an amplifier fails or fiber cut occurs, traffic must be rerouted through a new path. When a transmitter or receiver fails, the traffic must be transferred to different transmitter and/or receiver using the same or a different channel and/or transmission path.
Service providers have developed protection schemes to ensure service quality and provide automatic traffic restoration upon a failure in a transmission link. In some instances, redundant equipment systems are employed to decrease the effective failure rate of the link. Protection schemes generally are categorized based on the relationship between a working channel that carries traffic during normal operation and its corresponding protection channel that carries traffic if the working channel is unavailable. If traffic is transmitted simultaneously on both the working channel and the protection channel, the schemes are referred to as providing one plus one (“1+1”) protection. Conversely, if traffic is switched from the working channel to the protection channel or from a working path to a protection path only when a failure occurs, the schemes are referred to as one for one (“1:1”) protection schemes. More generally, N protection channels or paths can be shared between M working channels or paths, which is generally designated as N:M protection. Similarly, N protection channels can carry the same information as the working channel to provide 1+N protection.
In the event of a failure of one direction of the working path, a destination node for the traffic will switch to the protection path to receive the traffic in 1+1 schemes. In 1:1 schemes, origin and destination nodes are switched to the protection channel in path switched schemes, while nodes adjacent to the failure are switched in line and span switched schemes to route traffic around the failure. Various combinations of path, line, and span switching schemes can also be employed in 1:1 schemes.
In addition, failures in a network are detected by various local controllers in the nodes and must be communicated to the other nodes via the network management systems. The latency involved with providing notification throughout the network via the network management system can complicate and decrease the efficiency of the protection process.
As the demand for transmission capacity continues to grow, there is an increasing need to efficiently use the available transmission capacity and protect the information being transported through the systems. In addition, the increased amount of traffic being carried on each fiber places increased importance on the ability to protect the information effectively, because each failure results in higher revenue losses for service providers. Accordingly, there is a need for optical transmission protection schemes and network configurations that provide effective protection with increasing wavelength efficiencies for use in long distance communication systems.
The continuing interest in developing new filters with improved filtering characteristics is based on the recognition that wavelength separation technology still poses a limitation to the development of higher performance, lower cost communication systems. As such, there is a need to improve continually the optical filters and filtering methods available for use in optical components, subsystems and systems.